Micro-electromechanical systems (MEMS) are systems which are typically developed using thin film technology and include both electrical and micro-mechanical components. MEMS devices are used in a variety of applications such as optical display systems, pressure sensors, flow sensors, and charge-control actuators. MEMS devices of some types use electrostatic force or energy to move or monitor the movement of micro-mechanical electrodes, which can store charge. In one type of MEMS device, to achieve a desired result, a gap distance between electrodes is controlled by balancing an electrostatic force and a mechanical restoring force.
MEMS devices designed to perform optical functions have been developed using a variety of approaches. According to one approach, a deformable deflective membrane is positioned over an electrode and is electrostatically attracted to the electrode. Other approaches use flaps or beams of silicon or aluminum, which form a top conducting layer. For such optical applications, the conducting layer is reflective while the deflective membrane is deformed using electrostatic force to direct light which is incident upon the conducting layer.
More specifically, MEMS of a type called optical interference devices produce colors based on the precise spacing of a pixel plate relative to lower (and possibly upper) plates. This spacing may be the result of a balance of two forces: electro-static attraction based on voltage and charge on the plates, and a spring constant of one or more “support structures” maintaining the position of the pixel plate away from the electrostatically charged plate. One known approach for controlling the gap distance is to apply a continuous control voltage to the electrodes, where the control voltage is increased to decrease the gap distance, and vice-versa. However, precise gap distance control may be affected by several factors, including variations in the operating temperatures experienced by the interference device, the voltage applied to the interference device, material variations between support structures and other system variations.
One known method of calibrating an interferometer device is to use analog control circuitry to produce a continuously variable voltage, which is applied to the pixel plate and the electrostatically charged plate of the interferometer device, e.g., a bottom plate. Calibration of the applied voltages corresponding to various colors is done using a color sensor that uses color filters and corresponding photosensors to find the colors of the reflected light.